Triglyceride refining process



Patented Feb. 4, 1947 UNITED STATES PATENT o lcn Edward S. Liebscher, North Bergen, N. J.

No Drawing. Application January 19, 1942,

Serial No. 427,328

1 My invention relates to a refining process particularly adapted for refining vegetable and animal (including fish) oils and animal fats. Hereinafter in referring to this entire group I am designating them simply as oils. 1

The primary objects in refining vegetable and animal oils and fats are to remove free fatty acids therefrom, and to improve their color by the destruction or precipitation of coloring matters present therein. To attain these objects it is customary to mix the oil to be refined with an aqueous solution of caustic soda or soda ash or other suitable alkali. An aqueous solution of soda ash is sometimes used, although the caustic soda is usually preferred. Other alkalies, such as other hydroxides of alkali metals and of the alkaline earth metals, could be used in lieu of caustic soda and soda ash; but the latter are preferable for reasons well understood in the trade. The oil or fat to ,be refined is mixed with the alkali either in a kettle or in a mixer forming part of a continuous treatment apparatus and the alkali neutralizes (or saponifies) the fatty acids to form foots or soap stock which must be separated from the neutral oil. In these conventional processes the alkali attacks and saponifies variable amounts of the neutral oils due partly to local excess of alkali even with the best mix- .ing apparatus and due partly to the relatively large excess of alkali in the entire mass.

Where the process is carried out in kettles, the foots settle slowly and the neutral oils are drawn off from above the settled foots. In thecontinuous process this separation is ordinarily efiected by means of a centrifuge, but in both instances an appreciable proportion of the neutral oils is entrapped in the foots and is not readily recoverable therefrom.

The foots obtained as a lay-product of the ordinary treatment of an oil with alkali take the form of a watery, mobile sludge, containing particularly soaps, proteins or their split products, coloring matter or the degradation products, unused or excess alkali, glycerine resultingfrom the saponification of some of the neutral oil, and en-' trained or entrapped oil and air.

I designate as primary foots the foots which appear and settle out during the initial stages of kettle refining, in which I practice my invention. These primary foots are similar in composition to the foots of the prior art, except that my primary foots contain the added glycerine, but lower amounts of water, free alkali, entrained oil and glycerine resulting from saponification of neutral oil. By reason of their content of glycerine, together with their lower content of Water and of entrained oil, my primary foots exhibit a pasty or Waxy consistency. This quality contributes to a markedly sharper separation of my primary 'foots from the supernatant oil than is ch- 12 Claims. (Cl. 260-425) 2 tainable from the mobile and slushy foots of the prior art.

At later stages in the practice of my process, wherein my primary foots are made to yield up entrained oil, they are transformed, successively,

' into residues which I designate, respectively, as

secondary foots and tertiary foots. In general, the secondary foots and tertiary foots diifer in composition from the primary foots by containing successively smaller amounts of entrained oil.

An object of my invention is to provide an improved refining process whereby the amount of alkali required is reduced over that used in present processes.

Another object of my invention is to provide an improved process which will recover a larger proportion of the neutral oils.

Another object of my invention is to provide an improved process which can be carriedout either as a step by step or continuous process.

Another object of my invention is to provide an improved process which reduces the time required to refine the oils or fats.

Another object of my invention is to provide an improved process which reduces, refining losses. The difference betweenthe initial Weight of a crude oil and the weight of refined oil obtained therefrom represents the refining loss. Such a refining loss ordinarily is stated in per cent of the initial weight of crude oil subjected to a given refining operation.

Another object of my invention is to provide an improved process which is more economical than the processes now in use.

Another object of my invention is to reduce refining losses by reducing the saponification of neutral oils.

Another object of my invention is to reduce refining losses by removing substantially all of the oil entrained in the foots. 1 i

Other objects and advantages of my invention will become apparent as the description proceeds.

I attain the several objects and advantages of my present invention by using glycerine in addition to the alkali of the known methods. I may use other types of polyhydric alcohols, such as the glycols.

I have discovered that the high viscosity of glycerine, its general immiscibility with oils and fats and its marked aflinity for water combine to effect the following advantageous results in the practice of my present process.

(a) The presence of the glycerine disperses the active elements; of the alkali more thoroughly throughout the entire mixture so that these active elements more uniformly and quickly attack the fatty acids in the oil or fat. This more uniformdistribution. and thorough dispersion of the active elements of the alkali produces a quicker. and more uniform neutralization of the weight of crude oil,

(b) The affinity of the glycerine for water markedly reduces the property possessed by soaps of hydrating with large proportions of water especially in the presence of even small amounts of free alkali. The lessened degree of hydration of the soap particles-in this case neutralized fatty acids-is of at least two-fold advantage. First, the emulsifying action of the neutralized fatty acids on portions of the neutral oils is restricted, thus facilitating the coalescence of soap particles, initially of ultramicroscopic dimensions, to form visible clumps. Secondly, the lower degree of hydration'of the soap particles results .in' a higher specific gravity or: density thereof and contributes, in turn, to amarkedly greater settling rate of the primary foots. This important acceleration in the rate of settling of the primary facts I attribute also to the fact that my use ofthe relatively heavy glycerine-which obviates the prior-art requirement of an excess of water-increases the density of the primary roots as a whole. The rapid settling of the primary foots contributes greatly to the saving of time, which is an important advantage where my process is used in the kettle refining of oils.

As stated hereinbefore, entrained oil is recoverable only-with difficulty from the foots of the prior art. In my primary foots, however, the relatively unstable emulsion of entrained oil, due to the presence of water-avid glycerine, breaks down when these foots are heated to a melting temperature from about 165 to 195 so that the minute globules and films of entrained oil coalesce and, in substantial quantity, separate from, or are extruded by, the foots.

This heating of ,the primary foots to a melting temperature of 165 to 195 F. I preferably perremainder of the oil originally entrained in-the primary foots and form final or tertiary foots.

. The oil separated from the primary foo-ts'adds itself to the supernatant oil in the refining kett1eas will appear hereinafter in connection with thedescription of my preferred practice as applied to kettle refiningQTheoil separated from thesecondary foots may be collected in any suitable manner. Thereafter it ordinarily is added to the bulk'of refined oil. v

The accepted theoretical weight of NaOH requiredto neutralize the fatty acids in a crude oil is calculated by multiplying the weight of fatty acidspreviously determined bychemical anal sisby the factor 0.142. In the; practice of my process I also use this factor.

In order to reduce thecolor in the crude oil it is customary to use an additional quantity or excess of NaOH over, that needed to neutralize the fatty acids. This excess of NaOH ranges from about 0.3% to as high as about 1.0% of the weight. of the crude oil. 1 In the practice of my process, howeverpl do not employ so large an excess of NaOI-I, limiting it ordinarily to a quantity ranging from about 0.05% to 0.25% of the With certain oils, however, I may use an excess of Na-OII amounting to as much as 0.35% of the weight of crude oil. In any event, however, I use a lower excess of NaOl-l than would be used in refining of the same oil by known methods.

I consider to be a material factor in the reduction of refining losses which I obtain with my process, since there is less chance for saponification of neutral oil by the alkali.

In the commercial practice of my invention I V commonly employ the 45 to 50 per cent by weight of liquid caustic soda whi .1 is obtainable in tankcar lots. I may, however, dissolve solid NaOH in water containing the predetermined quantity of glycerine, calculated in the manner indicated hereinbelow, or I may employ an aqueous solution of NaOI-I made up in any suitable manner. In the case of the commercial liquid caustic soda, I employ a quantity thereof which contains the predetermined total requirement of NaOI-I'for the refining operation. This quantity I dilute with water until the solution commonly contains from about 7% to about 15% llaOH by weight. I may, however, use the predetermined total requirement of NaOI-I as a solution having a concentration ranging from about 5.0% to about 10% NaOH by weight.

The computation of the total requirement of NaOI-Ifor the refining of say 60,000 pounds of oil, may be illustrated by using the figure for free fatty acids of 1.6% by Weight and the figure for excess of NaOI-I of 0.175% by weight as given hereinbelow under Example 1.--Crude cotton oil.

The product of 1.6% and the factor 0.142, or

the 60,000 pounds of crude 011. But to this figure of 0.2272% there is to be added the chosen excess of 0.175%a total of 0. l022%. The total require ment, in pounds, of NaOI-I is, therefore, 60,000 times 0.004022, or 241.32 pounds. This'weight-(or more strictly, 241.36 pounds) of NaOHwould be present in 1871 pounds of a caustic soda solution containing 12.9% NaOH.

The weight of gylcerine which I employ-expressed as absolute glycero1is from about 0.5% to about 2.5% of the weight of oil to be refined. Although a higher ratio of glycerol to oil than 2.5% may be used, the additional quantity does not improve the refining operation to a material degree. I consider 0.5% of glycerol to be the safeminimum ratio thereof. In practice I commonly make use of a commercial grade of glycerine, ordinarily one containing about 83% by weight of glycerol. In consequence, I mix with the solution of NaOI-I, which I intend to employ in a particular refining operation, a weight of the 38% glycerine ranging from about 0.57% to about 2.8% of the weight of oil toberefined.

To illustrate the computation of the weight of 5 glycerine to be taken for the treatment of 60,000

pounds of oil, I return to the figures given hereinbelow under Example 1.--Crude cotton oil.

There it is stated that the refining solution was designed to provide 1.1% of glycerol. This 1.1%

of glycerol would be'equivalent to 1.25% of crude Consequently, the.

This lowered requirement of NaOH, brought about by the use of glycerine,

mixing the solution of NaOH and the glycerine separately with the oil to be refined, butas I have indicated above-I prefer to intermix them thoroughly, and then to incorporate the mixture, as a single refining solution, with the oil.

The commercial practice of kettle refining by my process I carry but preferably in the following manner:

A large quantity of crude oi1ordinarily a tank-car lot which, in trade usage, means 60,000 pounds of oilis pumped into a steam jacketed kettle or one fitted withclosed steam coils. The kettle contains the usual agitators. Agitation of the oil is started and the refining solution of alkali, water and glycerine, described above, is added to the oil-preferably in fine showersand rapidly incorporated therewith. The mixture'is brought rapidly to a temperature of about 130 to 150 F. As soon as the break, separation or seeding of primary foots appears, the agitation is stopped and these foots are allowed to settle, the above temperature being maintained for about an hour. If, however, the break be observed before all of the calculated quantity of refining solution has been added to the oil, the agitation is continued during the addition of the refining fluid, and for about one to two minutes thereafter. Then the agitation is stopped immediately. In either event, after stoppage of agitation the primary foots .are allowed to settle while a temperature of about 130 to 150 F. is maintained during the settling operation, which ordinarily takes about an hour. Immediately thereafter, the temperature in the kettle is increased to about 165 to 105 F., and maintained thereat for about fifteen to thirty minutes, after which the kettle and its contents are permitted to cool.

This heating effects a complete melting of the primary foots and this melting and the subsequent cooling expels therefrom a substantial amount of the entrapped oil and air, whereby the resulting or secondary foots are more compact. The extruded oil mixes with supernatant oil present in the kettle.

The removal of the bulk of refined oil from the refining kettle may be effected after the formation of the secondary foots, or after complete settling of the primary foots, or supernatant refined oil may be syphoned, decanted, or pumped,

from the kettle in the course of the settling of the primary foots.

The recovery of the entrained oil remaining in the secondary foots may be effected by treatment thereof in the refining kettle after removal of the supernatant oil. I prefer, however, to make the refining kettle available as rapidly as possible for the next batch of oil; and so I transfer the secondary ioots to a suitable tank or kettle for further treatment. In this way, in a 24-hour period I have refined three batches, approximating 180,000 pounds of crude oil, in a singlekettle; whereas by prior art methods of refining only one batch, approximating 60,000 pounds of crude oil, can be refined in the same time.

To efiect removal of entrained oil from the secondary foots, they are heated to complete fluidity, at about 165 to 195 for a period of about fifteen to thirty minutes. An initial quantity of oil separates from these foots, and then, as cooling takes place, substantially all of the remaining entrained oil is extruded, leaving a final residue of tertiary foots. The oil recovered from the secondary foots then is added to the- Soap-making art; and then is available for use in the further practice of my process.

In the kettle, as well as in the continuous method ofrefining certain types of oils or crude oils of certain grades, I sometimes find it advantageous to heat the oil to about to 159 F. before adding the refining solution.

In the practice of my invention by a continuous method the initial steps are substantially those which I use in kettle refining, namely, agitating the crude oil-either in the cold or after heating to about 130 to F.with a predetermined quantity of refining solution and continuing for approximately two minutes the agitation of the mixture after the temperature of the latter, if not heated theretofore, has been brought rapidly to the temperature of about 130 to 150 F. The mixture then is passed to centrifugals to eifect separation of the refined oil from the fOOts. The foots obtained after centrifugation are substantially free of oil and are ready for recovery of the glycerine present therein.

The following two examples show the reduction in refining losses which I efiect by the practice of my invention:

Example 1.C'rude cotton all One tank car of crude cotton oilcontaining 1.6% of free fatty acids was kettle refined by my process with a solution designed to provide 1.1% of glycerol and an excess of 0.175% NaOl-I, as explained hereinabove. comprised 1871 pounds of caustic soda solution, containing 12.9% NaOl-I, in which were dissolved 750 pounds of crude glycerine (88%). The refining loss was 3.78%. A tank car of the same oil kettle refined by the prior art process showed a refining loss of 5.8%.

A tank car of the. same oil after treatment by the continuous method usin my invention and with the same quantity and character of refining solution, including glycerine, thatwas used in my novel kettle refining process hereinabove described, showed a like refining loss of 3.78%. A tank car of the same oil, after treatment by the continuous method of the prior art, showed a refining loss of 4.66%.

E$ample 2.--C'rude soybean oil A tank car of crude soybean oil, containing 0.55% free fatty acids was kettle refined by my process with a solution designed to provide 1.0% of glycerine and an excess of 0.179% of NaOI-I. The refining solution comprised 161'? pounds of caustic soda solution containing 9.54% NaDH, in which were dissolved 684 pounds of crude glycerine (83%). The refining loss was 2.20%. A tank car of the same oil, kettle refined by the prior art process, showed a refining loss of 6.25

A tank car of the same oil, after treatment by the continuous method, using my novel process, with the same quantity and character of refining solution, including glycerine, that was used. in my novel kettle refining, showed a like refining loss of 2.20%. A tank car of the same oil, after continuous refining by the prior art process, showed a refining loss of 4.25%.

My invention is not to be construed as limited The refining solution.

apparatus and different techniques.

to its use with the specific apparatus herein referred to nor to the details of the specific examples given, since my novel process may be carried out with any conventional or suitable apparatus and will vary in detail for different oils, different And the scope of my invention is determined'by the following claims.

I claim: i a

1. The process of kettle refining of oils which comprises preparing an aqueous solution of caustic soda in a concentration of about to 18% by weight of sodium hydroxide and containin suificient sodium hydroxide to neutralize the fatty acid in the oil to be refined plus an excess of sodium hydroxide equal to about 05% to .35% of the weight of said oil, adding to said aqueous solution a weight of glycerol equal to about .5%

to 2.5% of the weight of said oil to form a refining solution, the glycerol thereof causing a decrease in the hydration, and an increase in the density and oil-separability, of the foots formed by the interaction of the oil and the alkali in the refining solution, mixing said oil with said refining solution and raising the temperature of the mixture to about 130 F. to 150 F., stopping the mixing upon the appearance of primary foots, permitting the primary foots to settle and removing the refined oil while maintaining said temperature, expelling the refined oil from the primary foots to produce secondary foots by subjecting the primary foots' to a temperature of about 165 F. to 195 F. for about 15 to minutes and permitting them to cool and drawing off the oil expelled from the primary foots, expelling re- 1 fined oil from the secondary roots to form tertiary foots by subjecting the secondary foots to a melting temperature of about 165 F. to 195 F. for about 15 to 30 minutes and permitting them to cool and removing the supernatant oil, and treating the tertiary foots to recover glycerol therefrom and reusing said recovered glycerol in the process.

2. The process of kettle refining of oils which comprises preparing an aqueous solution of caustic soda in a concentration of about 5% to 18% by weight of sodium hydroxide and containing sufficient sodium hydroxide to neutralize the fatty acid in the oil to be refined plus an excess of sodium hydroxide equal to about 05% to of the weight of said oil, adding to said aqueous so-,

lution a weight of glycerol equal to about .5% to 2.5% of the weight of said oil to form a refining solution, the glycerol thereofcausing a decrease in th hydration, and an increase in the density and oil-separability, of the foots formed by the interaction of the oil and the alkali in the refining solution, mixing said oil with said refining solution and raising the temperature of the mixture to about 130 F. to 150 F., stopping the mixing upon the appearance of primary foots, permitting the primary foots to settle and removing the refined oil while maintaining said temperature, ex-

V polling the refined oil from the primary foots to produce secondary foots by subjecting the primary roots to a temperature of about 165 F. to 195 F. for about 15 to 30 minutes and permitting them to cool and drawing off the oil expelled from the primary ioots, and expelling refined oil. from the secondary foots to form tertiary pfoots by subjecting the secondary facts to a melting temperature of about 165 F. to 195 F. for about 15 to 30 minutes and permitting them to cool and removing the supernatant oil. i

3. The process of kettle refining of oils which comprises preparing an aqueous solution of caus tic soda in a concentration of about 5% to 18% by Weight of sodium hydroxide and containing sufficient sodium hydroxide to neutralize the fatty acid in the oil to be refined plus an excess of sodium hydroxide equal to about .05% to 35% of the weight of said oil, adding to said aqueous solution a weight of glycerol equal to about .5% to 2.5% of the weight of said oil to form a refining solution, the glycerol thereof causing a decrease in the hydration, and an increase in the density and oil-separability, of the foots formed by the interaction of the oil and the alkali in the refining solution, mixing said oil with said refining solution and raisin the temperature ofthe mixture to about F. to F., stopping the mixing upon the appearance of primary foots,

permitting the primary roots to settle and removing the refined oil whilemaintaining said temperature, and expelling the refined oil from the primary foots to produce secondary foots by subjecting the primary foots to a temperature of about to F. for about 15 to 30 minutes and permitting themto c001 and drawing ofi the oil expelled from the primary foots.

4. The process of kettle refining of oils Which comprises preparing an aqueous solution of caustic soda in a concentration of about 5% to 18% by weight of sodium hydroxide and containing sufiicient sodium hydroxide to neutralize the fatty acid in the oil to be refined plus an excess of sodium hydroxide equal to about .05% to .35% of the Weight of said oil, adding to said aqueous solution a weight of glycerol equal to about .5% to 2.5% of the weight of said oil to form a refining solution, the glycerol thereof causing a decrease in the hydration, and an increase in the density and oil-separability, of the foots formed by the interaction of the oil and the alkali in the refining solution, mixing said oil with said refining solution and raising the temperature of the mixture to about 130 F. to.

150 F., stopping the mixing upon the appearance of primary foots, permitting the primary foots to settle and removing the refined oil While maintaining said temperature, and expelling the refined oil from the primary foots to produce secondary foots by subjecting the primary foots to a temperature of about 165 F. to 195 F. and permitting them to cool and drawing off the oil expelled from the primary foots;

5. The process of kettle refiningof oils which comprises preparing an aqueous solution of caustic soda in a concentration of about 5% to 18% by Weight of sodium hydroxide and containing sufiicient sodium hydroxide to neutralize the fatty acids in the oil to be refined plus an excess of sodium hydroxide equal to about .05% to 35% of the Weight of said oil, adding to said aqueous solution a weight of glyceroliequal to to settle and removing the refined oil while main- 7 taining said heat, and expelling the refined oil from the primary foots to produce secondary foots by melting the primary foots and permitting them to cool'and drawing off the oil ex pelled from the primary foots.

6. In the process of kettle refining of oils, wherein the oil is mixed, at a temperature not exceeding about 150 F., with an alkaline r fining solution containing a quantity of glycerol equal to about .5% to 2.5% of the weight of said oil, the glycerol causing a decrease in the hydration, and an increase in the density and oil-separability, of the foots formed by the interaction of the oil with the refining solution, and the mixing is stopped upon the appearance of primary footsthe steps of permitting the primary foots to settle while maintaining said temperature and removing the refined oil, thereafter melting the primary foots and permitting them to cool, thereby formin secondary foots, and separating therefrom the oil expelled from the primary foots.

7. In the process of kettle refining of oils, wherein the oil is mixed, at a temperature not exceeding about 150 F., with an alkaline refining solution containing a quantity of glycerol equal to about .5% to 2.5% of the weight of said oil, and the mixing is stopped upon the appearance of primary roots-the steps of permitting the primary foots to settle and removing the refined oil while maintaining said temperature, the glycerol causing a decrease in the hydration, and an increase in the density and oil-separability, of the foots formed by the interaction of the oil with the refining solution, expelling the refined oil from the primary foots to produce secondary foots by subjecting the primary foots to a temperature of about 165 F. to 195 F. for about 15 to 30 minutes and permitting them to cool and drawing off the oil expelled from the primary foots, thereafter expelling refined oil from the secondary foots to form tertiary foots by subjecting the secondary foots to a melting temperature of about 165 F. to 195 F. for about 15 to 30 minutes and permitting them to cool, and removing the oil expelled therefrom.

8. In the process of kettle refining of oils, wherein the oil is mixed, at a temperature not exceeding about 150 F., with an alkaline refining solution containing a quantity of glycerol equal to about .5% to 2.5% of the weight of said oil, the glycerol causing a decrease in the hydration, and an increase in the density and oil-separability, of the roots formed by the interaction of the oil with the refining solution, and the mixing is stopped upon the appearance of primary foots-the steps of permitting the primary foots to settle and removing the refined oil while maintaining said temperature, thereafter expelling the refined oil from the primary foots to produce secondary foots by subjecting the primary foots to a temperature of about 165 to 195 F. for about 15 to 30 minutes and permitting them to cool, and drawing off the oil expelled from the primary f cots.

9. In the process of kettle refining of oils, wherein the oil is mixed, at a temperature not exceeding about 150 F., with an alkaline refining solution containing a quantity of glycerol equal to about .5% to 2.5% of the weight of said oil, the glycerol causing a decrease in the hydration, and an increase in the density and oil-separability, of the facts formed by the interaction of the oil with the refining solution, and the mixing is stopped upon the appearance of primary foots, the steps of permitting the primary foots to settle and removing the refined oil while maintaining said temperature, thereafter expelling the refined 10 oil from the primary foots to produce secondary foots by subjecting the primary foots to a temperature of about to and permitting them to cool and drawing off the oil expelled from the primary fonts.

30. The process of kettle refining of oils containing free fatty acids which comprises, mixing with the oil, in the presence of an elevated te r.- perature not exceeding about 150 F., (a) an aqueous refining solution containing an amount of alkali sufiicient to neutralize the fatty acids and to form refined oil and foots, and (b) an amount of glycerol suificient to decrease the hydration of, and to increase the density and oilseparability of, said foots, removing the refined oil from the foots, melting the foots and permitting them to cool, whereby to expel refined oil therefrom, and drawing off the refined oil formed along with the roots and that expelled therefrom.

11. The process of kettle refining of oilscontaining free fatty acids which comprises, mixing with the oil, in the presence of an elevated temperature not exceeding about 150 F., (a) an aqueous refining solution containing an amount of alkali sufi'icient to neutralize the fatty acids and to form refined oil and foots, and (b) a polyhydric alcohol, selected from the group consisting of glycerol and glycols, in amount sufficient to decrease the hydration of, and to increase the density and oil-separability of, said foots, removing the refined oil from the foots, melting the roots and permitting them to cool, whereby to expel refined oil therefrom, and drawing off the refined oil formed along with the foots and that expelled therefrom.

12. The process'of kettle refining of oils containing free fatty acids which comprises, mixing with the oil, in the presence of an elevated temperature not exceeding about 150 F., (a) an aqueous refining solution containing an. amount of alkali sufficient to neutralize the fatty acids and to form refined oil and foots, and (b) an amount of a glycol sufiicient to decrease the hydration of, and to increase the density and oilseparability or, said roots, removing the refined oil from the foots, melting the foots and per.- mitting them to cool, whereby to expel refined oil therefrom, and drawing off the refined oil formed along with the roots. and that expelled therefrom.

EDWARD S. LIEBSCHER.

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